1. Field of the Invention
The present invention relates to a hand-held drive-in tool for driving fastening elements in a workpiece, comprising a guide, a drive-in ram displaceable in the guide for driving a fastening element in, a drive-in unit for driving the drive-in ram and including at least one or first drive spring having a first expansion direction, and a tensioning device for preloading the drive-in ram and the at least one drive spring.
2. Description of the Prior Art
In the drive-in tools of the type discussed above, a mechanical drive spring, which is preloaded by a tensioning device, is used as a drive source. An advantage of this consists in that a mechanical drive spring is economical so that a drive-in tool with such drive spring can be economically produced. Further, an advantage of a mechanical drive spring in comparison with a gas spring consists in that preloading of a mechanical spring does not lead to a temperature increases, as with a gas spring. Therefore, the preloaded mechanical spring does not lose the stored energy, whereas in the gas spring, the energy is gradually lost.
The drawback of a mechanical spring in comparison with a gas spring consists in that the mechanical spring creates an increased portion of the rebound of the drive-in tool during a setting process.
A drive-in tool of the type described above is disclosed in German Publication DE 40 13 022 A1. In the known drive-in tool, a spring drives an impact mechanism for driving a nail toward the drive-in tool muzzle. An adjusting device for returning the impact mechanism in the initial position includes an electric motor and gear transmission mechanism therefor. The rotation of the electric motor is transmitted via the gear transmission mechanism and a cooperating with it, toothed disc to the hammer body of the impact mechanism in order to displace the impact mechanism against a biasing force of the drive spring in the initial position of the impact mechanism in which the impact mechanism is ready for a further impact process.
The drawback of the known drive-in tool consists in that the maximal impact energy applied by the spring to the hammer body is between about 5-10 Joule and is rather low. Therefore, this drive-in tool is not suitable for driving fastening elements in hard constructional materials, such as steel and concrete. If the impact energy of the drive-in tool is to be increased, a stronger spring should be provided that can store more energy. However, with this, the spring mass is also increased, which in turn increases the rebound of the drive-in tool.
Accordingly, an object of the present invention is to provide a drive-in tool in which the foregoing drawbacks are eliminated, and the rebound is small even with the use of stronger drive springs.